The Z80 also added two index registers (IX and IY) and relocatable vectored interrupts (via the 8-bit IVregister). Like many processors (including the 8085), the Z80 featured many undocumented opcodes. Chip area near the edge was used for added instructions, but fabrication made the failure of these high. Instructions that often failed were just not documented, increasing chip yield. Later fabrication made these more reliable.

The Z80 was used in the first NintendoGame Boy. A Sharp Z80 work-alike was used in the GameBoy Color, running at 4 MHz for GameBoy software or at 8 MHz for Game Boy Color software. The Z80 was used in the SegaMaster System and the Game Gear. It was also used in the Sega Genesis for hardware reverse compatibility with the Sega Master System through a special cartridge.